The present invention is directed generally to the fastener arts, and more particularly to a novel and improved tamper-proof drive system for fasteners. Still more particularly, the present invention is directed to an improved drive system of the multi-lobular configuration, for example, similar to the drive systems generally known in the trade as the TORX.RTM. and the TORX PLUS.TM. DRIVE SYSTEMS.
The well-known TORX.RTM. fastener and driver system is the subject matter of U.S. Pat. No. 3,584,667 comprises a generally six-lobed or "hexlobular" configuration wherein the curved surfaces which define the flutes and lobes are generated from arcuate configurations. The TORX PLUS.TM. drive system is also a multi-lobular configuration, however, with this particular system the flutes and lobes are generated using elliptical rather than arcuate geometric configurations. The TORX PLUS.TM. drive system is disclosed in U.S. patent application Ser. No. 07/777,644, filed Oct. 16, 1991. The disclosure of the TORX.RTM. U.S. Pat. No. 3,584,667 and said application Ser. No. 07/777,644 are incorporated herein by reference.
More particularly, these drive systems comprise complementary fastener drive heads and driving tools that define lobes and flutes centered about the six apices of a regular hexagon. These lobes and a similar series of intervening flutes or inwardly curved surfaces advantageously define a number of advantages, such as improved efficiency in converting applied force to driving torque due to the extremely low drive angles achieved, improved structural integrity due to a lower radial force components, etc., over other prior art drive systems.
With standard tamper-proof drive systems only drive tools specifically designed for complementary use with the fastener drive heads of the system may be successfully employed in rotating or driving the fastener. However, in a hexlobular system, such as the TORX.RTM. or TORX PLUS.TM. systems, this is not completely accurate. The generally symmetrical and regular hexagonal disposition of the internal lobes and flutes of the drive system results in diametrically opposed lobes and flutes. Accordingly, a conventional straight blade-type tool, such as a conventional screw drives could conceivably be inserted into the recess and utilized to rotate a fastener provided with such a drive head configuration. One solution to remedy this problem, is to prevent insertion of a blade-type drive tool by providing a post or cylindrical protrusion substantially centered in the recess of the drive head and a complementary central cylindrical recess is then formed in the driving tool. Hence, with such a protrusion and complementary recess, a standard blade-type tool could no longer be interfitted within a recessed drive head.
While the foregoing tamper-proof systems have found widespread acceptance, problems have been encountered in adapting this system to relatively small fasteners. More specifically, small fasteners that are often used for assembly of consumer electronic products employ even smaller drive heads and drive recesses and it has been found difficult and at times impossible reliably to form the necessary tamper-proof protrusions and corresponding recesses. In this regard, due to the small size of the drive tool, the removal of material to form a complementary recess removes so much material, that the strength of the tool is rendered insufficient for reliable and repeated operations. As to the fastener drive recess, the size of the post or protuberance that is required is so small that the post is difficult to form with standard cold heading processes, and even when formed is so structurally weak that it can be bent or fractured or otherwise rendered ineffective for its intended purpose. In contrast, the advantageous features of the TORX.RTM. and TORX PLUS.TM. drive systems are the reliability over a long service life, the efficient conversion of applied force to driving torque and attendant resistance to breakage and damage in long term operation of the drive tools.
As such, the present invention was developed to retain the advantages and improved features of the TORX.RTM. and TORX PLUS.TM. drive systems, yet provide a tamper-proof arrangement that can be used with relatively small fasteners.